Welcome!
Can't really go wrong with the featured stories on the main story list. "Anything by Endmaster" is the usual recommendation, but if you have a genre preference maybe we can narrow that down.
See this article
here for a list of longer games from the last couple years on a variety of subjects. These all have a low number of ratings due to taking a little while to get through, and I know the authors would appreciate the attention.
For writing, you can go to the Writing Workshop if you have any specific questions, but just for general advice, once you have your setting and characters decided on, do a bit of plannig on the plot and most importantly
keep it small. Attempting some gigantic epic right out of the gate is the number one cause of burnout for newbies. Everyone always massively underestimates how much work goes into any kind of choice based story.